Discharge tube cathode energizing



July 11, 1933. B. F. MIESSNER 1,917,728

DISCHARGE TUBECATHODE ENERGIZING Filed March 30, 1928 BY m ATTORN Y.

Patented July 11, 1933 UNITED STATES PATENT oFFIcE BENJAMIN r. minssnnn orsnonr nILLs, NEW JERSEY, ASSIGNOR, BYI MEsNE Assren- MENTS, ro name oonronarrou or AMERICA, or new YORK, N. Y., A CORPORATION f OF DELAWARE DISCHARGE TUBE GATI-IODE nnEnGIzING Application filed. March 30, 1928. Serial No. 265,922.

The present application is a substitute for a portion of my copending application Serial No. 30,163, filed, May 14, 1925, which in turn is a substitute for a portion of my original application Serial No. 57 8,07 9, filed July 28, 1922. The present invention, disclosed in both of the above referred to applications, relates generally to energizing the cathode or fila- 0 ment of vacuum and like discharge tubes with alternating current when such tubes are used in amplifying and detecting systems, and includes in particular soarrang ing and connecting the tubes in circuits as to permit them to act efiectively as amplifiers or detectors while avoiding in large measure hum effects of the alternating current.

Another particular object is to energize the cathode of a tube with alternating cur- 0 rent, and to so connect and further energize the tube that it can be used inconnection with an element responsive to audible frequency currents to effectively detect high frequency currents modulated at audible frequency while avoiding in large measure audible hum efiects from the alternating current.

Other objects of invention will appear as this description progresses, reference being had to the accompanying drawing, in which Figure 1 is a more or less diagrammatic illustration of a circuit and apparatus embodying my invention; and I Figures 2 and 3 are similar figures showing different forms of my invention,

Prior to my inventionas disclosed inthe above figures it wasthe general practice in the use of el ctron discharge apparatus comprising a heated cathode and an anode, and, in some instances, anauxiliary electrode usually designated a grid, to heat the cathode by direct current of substantially constant potential, as from a batteryor direct current generator. In general the connections of the circuits to the cathode have been made at one side or the other of the cathode heating circuit with the result that all parts of the cathode or filament have not had' the same potential with "respect to'the anode or grid, the difference being as-niuch as the total heating current potential impressed difference of potential is constant and does.

not produce any periodic current variations in the circuits connectedto the cathode.

It is convenient in many cases to employ alternating current for cathode energizing, but when'so energized connections of the anode or grid to one side of the heating current circuit produce periodic current and potential variations in the anode or grid circuits which variations can be intercepted in translating devices "as troublesome hum- For example, if a vacuum tube systemis' used for amplifyinggor rectifying weak high frequency signaling currents, as in radio, the effect of employing an alternating current for heating the cathode will be to set up periodic current and potential variations in the circuits of the system when the usual circuit connections to the filament heating system are used, the frequency of which variations is equal to the frequency of the heat ing current in cycles per second.v If the tube is an amplifier these variations may be amplified. The responsive devices usually employed in radio signaling, such as telephones, are highly responsive in the frequency range usual to commercial alternating current supply systems, wlth' theresult that hum efiects will be produced which may be undesirable, or seriously interfere with signaling. I V In'the embodiment of my invention llustrated in Figures 1, 2 and 3, I provide a source of alternating current for heating the filamentary cathodes of the tubes shown, but I so connect the plate and grid circuits ofthe electron discharge apparatus with'the' t lament system as to prevent the productlon of pulsations in the circuits of these elec-' trodes which would otherwise result from the use of alternating current for heating the cathode, and use'poten'tials independent of the heating circuit potentials for energizing the plate and grid electrode for desired operation as detector or amplifier or both. I

In Figure 1, i I disclose an electron distrated as comprising the winding 24 and the lized for radio reception the winding 2e may charge device comprising an evacuated receptacle 20 in which are mounted the filamentary cathode 21 and a plate anode 22, time apparatus being of well-known construction and designed to rectify the alternating currents flowing in the circuit 23 which is illusvariable capacity 25. The device 26 in the anode circuit indicates any responsive device requiring direct current for its operation, as a telepone. When the circuit is uticonstitute the secondary winding ofa transformer or coupling element 24 for coupling the circuit to an antenna circuit, or for interstage coupling for coupling the circuit to a preceding stage. Included in the circuit 23 may be a source of current 35 for placing a bias on the plate or grid as the case may be. This comprises a battery 36 bridged by a potentiometer 37. v The circuit wire 23 connects to the center of the battery 36 and the wire 38 leading to the device 26 may be connected through a shiftable contact to any desired point along the potentiometer 37 for obtaining either a positive or negative bias, thus determining the mode of operation of the tube.

For heating the cathode 21 I provide a source of alternating current comprising a trans ormer T having the primary Winding P and the secondary winding S. This transformer will usually be of the step-dovn variety to enable the filament 21 to be heated from the usual house circuits. Shunting' the terminals of both the secondary winding and the cathode is a resistance 27 which should be of such value as to assure substantially all of the secondary output of the transformer being delivered to the cathode. The resistance 27 is preferably provided with a sliding contact 28 which is connected with one terminal 23' of the alternating current circuit 23, the other terminal 23". of this circuit being connected with the terminal of the plate or anode 22.

In describing the mode of operation of my improved apparatus it is assumed that the cathode 21 requires a potential of six volts for properly heating it. This explanation may be more readily understood if it is assumed that at any one instant one terminal of thetransformerand the corresponding terminal of the filament has a potential of plus the potentials of the corresponding terminals head set. r

of thesecondary winding and the filament (disregarding drops in potential due to the resistance of the connecting leads).

By taking the connection for the circuit 23 from the electrical center of the balancing resistance 27, where the potential variations are substantially nil, the periodic variations of the alternating current is eliminated from the circuit 23, leaving only the steady potential of battery 36 for energizing the anode in the right way to produce the best rectifying eiiect for detection. By virtue of the adj'ustability of the slidable contact 28 along this resistance 27, the adjustment for best results can be easily and quickly obtained. Attention is also directed to the fact that the resistance 27 has substantially no react-ance. to high frequencies traversing thc circuit 23. It thus offers no disturbing 11'11 pedance 0r reactance to radio frequencies native arrangement I have shown the secondary S as being shorted by a shunt 27 whichcomprises two condensers 31 and 32 which are connected in series, one terminal 23 of the high frequency circuit being connected with the shunt- 27 at a point intermediate the condensers 31 and 3;, which point will have the same potential as electrical centers of the secondary winding and thefilament, respectively. Conduction between the filament circuit and the outer circuit 23 occurs substantially the same as that shown in Figure 1, except the high frequency currents flowing in the circuit 23 pass to the filament by electro-static action rather than ree by direct conduction, as in Figure 1. As oescribed of the resisance 27 the condenser shunt 27 will interpose substantially no reactance to high frequencies.

In the plate circuit of this embodiment is included a battery lland reproducing means 26, such as a loud speaker or usual telephone A condenser 12 may be shunted across this reproducing means. In producing the electrical oscillations in this circuit,

as for heterodyne reception, I make use of a I.

tickler coil llinduc 'ively related to the winding 24:, and operating in conjunction wlth the tube to perform a regeneratlng function. This tickler coil also serves to amplify the currents passed through the tube. The coil 24 may be inductively coupled to an antennacircuit or through interstage coupling to a preceding stage, as I have before described. A rheostat 46 may be'interposed in the filament circuit. As described in connection with Fig. 1, the battery 36 and potentiometer 37 permit of energizing the electrode to which connected, in this case the grid, independently of the filament heating circuit for desired operation of the tube, as for amplification, detection, or both.

In the construction shown in Figure 3, which illustrates a simple radio receiving circuit, current is supplied to the cathode 21 by the secondary winding S of the transformer, just as in the preceding arrangement, but in this construction the cathode is provided with a third external terminal 33 which connects with the center. of the filamentary cathode and the alternating current or high frequency current circuit 23. The theory of operation of this circuit is analogous to that of the preceding circuits and further explanation thereof appears to be unnecessary.

I do not intend to be limited to the particular details and circuit connections herein described, as it will be evident that the broad features of my invention can be practiced by other apparatus and other circuit connections than those specifically shown.

I claim:

1. In a system for receiving high frequency electrical signals modulated at audible frequency including means for amplifying said signals, means for detecting said signals including a three electrode vacuum tube and a device responsive to audible frequency current components associated with the output circuit of said tube, means for energizing the filament of said tube with alternating current energy, means for connecting a high fre qucncy input circuit to the grid electrode and filament system of said tube so as to be substantially independent of the alternating current potentials employed for energizing said filament, and independent means for energizing the grid electrode of said tube for operation as a rectifier, whereby disturbing hum production in said audible frequency responsive device is materially avoided.

In asystem for receiving high frequency electrical signals modulated at audible frequency including a three electrode vacuum tube having a heated cathode, means responsive to audible frequency current components associated with the output circuit of said tube, means for heating the cathode of said tube with alternating current energy, a high frequency signal receiving circuit connected between said heated cathode and the grid electrode of said tube so as to be substantially independent of the alternating current potentials employed in the heating of said cathode, and independent means for energizing said grid electrode With respect to said cathode to produce desired operation of said tube, whereby disturbing hum production in said means responsive to audible frequency currents is materially avoided.

3. In a system for receiving high frequency electrical signals modulated'at audible frequency including a three electrode vacuum tube having a heated cathode, means responsive to audible frequency current components associated with the output circuit of said tube, means for heating the cathode of said tube with. alternating current energy, a high frequency signal receiving circuit connected between the cathode heating system and the grid electrode of said tube so as to be substantially independent of the alternating current potentials employed in the heatingof said cathode, and independent means for en ergizing said grid electrode with respect to aid cathode for causing said tube to make the received modulated high frequency signal energy effective on said responsive means.

4:. In a system for receiving high frequency electrical signals modulated at audible frequency, the combination of a three electrode vacuum tube having a hot cathode, a system for heating said cathode with alt-ernating current energy, a high frequency signal recelving circuit connected between the cathode heating system and grid electrode of said tube so as to be substantially independent of the alternating current potentials employed in the heating of said cathode, an output circuit connected between the plate electrode of said tubeand said cathode heating system so as to be substantially independent of the alternating current potentials employed in the heating-of said cathode, means responsive to audible frequency current components associated with said output circuit, and independent means in both of said circuits for energizing the grid and plate elec-- trodes of said tube to cause it to function as an efficient rectifier of the high frequency signal energy for action on said responsive means.

In witness whereof, I hereunto subscribe 

